User:R. Jeremy Johnson/Sandbox 1

 Ribonuclease A - Structure 7RSA 

Background
This structure of Photosystem II was crystallized from the cyanobacteria, Thermosynechococcus elongatus, at 3.0Å and at 3.50 Å. PDB codes are 2axt and 1s5l, respectively. Cyanobacteria and plants both contain Photosystem II while photosynthetic bacteria contain the bacterial reaction center. This photosynthetic protein complex is associated with a variety of functional ligands. It is a dimer composed mainly of alpha-helices. Nineteen subunits are in each monomer, with multiple extrinsic subunits associated with the oxygen evolving complex missing from this crystallization. Photosystem II is a membrane bound protein complex that in plants is associated with the thylakoid membrane of chloroplasts. Polar and hydrophobic regions correlate with membrane associated nature of the protein. Hydrophobic helices make up the transmembranal portion, while polar residues are concentrated externally on either side of the membrane.